There are many applications in workpiece manufacture and parts assembly where a cam-actuated drive device is needed to provide both lift and translation movements. For example, walking beam assemblies need a drive which will both lift a part or tooling nest from one work station location, proceed through translation, i.e. horizontal movement, to a second location, and then lower the part or tooling nest to a second work station. Alternatively, such two direction drives can be utilized to progressively move conveyor systems, such as where a pair of fingers are moved outwardly to a first direction to engage, i.e. mechanically "spear", a segment of a conveyor belt system, the pair of fingers are then translated linearly along a second direction (and thereby move all sections of the conveyor from a first to a second position), next they are retracted from the conveyor system, and then are linearly moved back to a "start" or home position. In that fashion, such a conveyor drive unit operates to continuously index the conveyor forward section by section. Yet further, such two-direction drive devices can be used as part transfer mechanisms in pick-and-place assembly units.
However, unless protected, such two-direction, cam-actuated drive devices are unfortunately subject to damage should, for example, a jam occur, such as in the associated tooling, or with the tooling mounting block that is driven by the drive device. Thus, whether in a vertical lift (i.e. extension) mode, or a vertical retract (i.e. lowered) mode, or in either of the horizontal translation modes, such drive devices can suffer serious damage should jams occur. This can include damage to the roller followers, or directly to the drive cam members Thus, such unprotected cam-actuated drives are always subject to damage, even when micro switch-type overload protection sensors are used with the associated tooling.
Accordingly, there is a ongoing need for a protected, cam-actuated drive device for use with walking beam assemblies. One such known drive, with protection against jam-created damage available in one vertical direction, is manufactured and distributed by Stelron Components, Inc., of Hahwah, N.J.; it is sold under Stelron trademarks "ST" and "SBT" Translator series. (An older, "unprotected" version is sold under Stelron's "T Series" trademark.) However, this prior design for protected cam-actuated drives has several disadvantages. First, the carriage assembly (through which the respective lift rods oscillate and which itself oscillates along the horizontal translation guide bars), is of a relatively short width, i.e. short span. That, in turn, affects the overall stability of the associated tooling. Second, the available translation stroke, i.e. horizontal movement, as provided by such a prior design is compromised by the fact that there is blocking structure, i.e. lift cam and bell crank structure, that obstructs any otherwise full horizontal translation of the carriage (in the extension direction). That is, because the lift arm structure sits out to the side of the lift barrel cam, it partially blocks the carriage's extension movement.
Third, with such prior devices, there is spring protection (against jams) provided only in the Y (vertical) axis, i.e. none along the X (horizontal translation) axis. Further, the available Y axis spring protection is limited to the raised or extension mode, i.e. no spring protection is available in the lowered or retraction mode.
Fourth, even with such prior (Y axis) "protected" walking beam drive designs, the protection spring structure is, at least partially, outwardly exposed to the operating environment. That presents potential human safety concerns, i.e. one's fingers can be caught up in the spring area. Further, potential damage can occur to such exposed spring structure, such as by broken parts, jammed tooling, and the like. Also, if they become broken, spring parts flying about could present a safety hazard.